Optoelectronic component and method for producing an optoelectronic component

ABSTRACT

An optoelectronic component and a method for producing an optoelectronic component are disclosed. In an embodiment an optoelectronic component includes at least one optoelectronic semiconductor chip configured to emit radiation and an encapsulation around the semiconductor chip. The encapsulation is a polysiloxane. A barrier layer can be used for protection against harmful gases, the barrier layer being arranged on the encapsulation. The barrier layer is a plasma-polymerized siloxane layer.

This patent application is a national phase filing under section 371 ofPCT/EP2019/051266, filed Jan. 18, 2019, which claims the priority ofGerman patent application 102018101710.3, filed Jan. 25, 2018, each ofwhich is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The invention relates to an optoelectronic component. The inventionfurther relates to a method for producing an optoelectronic component.

BACKGROUND

Optoelectronic components often have encapsulations which have a certaingas permeability. For this reason, harmful gases, such as volatileorganic compounds (VOCs), can permeate the encapsulation and reach thesurface of the semiconductor chip of the optoelectronic component. Theradiation emitted by such a semiconductor chip in combination with thelocally increased temperatures in the vicinity of the semiconductor chipfinally lead to the decomposition and deposition of the harmful gasesinside the optoelectronic component. This results in a loss ofbrightness, for example due to carbon depositions resulting from thedeposition of VOCs in the beam path of the component. Such anoptoelectronic component then emits light with reduced brightness and ina different light color. The optoelectronic component is thus not stablein the presence of the harmful gases.

SUMMARY

Embodiments provide an optoelectronic component that is stable againstharmful gases such as VOCs. Further embodiments provide a process forproducing an optoelectronic component which produces a component stableagainst harmful gases.

In at least one embodiment, the optoelectronic component comprises atleast one optoelectronic semiconductor chip, which is designed to emitradiation. For example, the optoelectronic component can have exactlyone semiconductor chip. For example, the semiconductor chip can emitelectromagnetic radiation in the UV wavelength range or in the bluespectrum of visible light.

In at least one embodiment, the optoelectronic component comprises anencapsulation. The encapsulation is arranged around the semiconductorchip, i.e., at least partially encloses it. For example, thesemiconductor chip can be arranged on a substrate and the encapsulationencloses the semiconductor chip on the substrate. For example, theencapsulation and the substrate can together completely surround thesemiconductor chip. Similarly, the semiconductor chip may be arranged inan indentation of a package so that the package together with theencapsulation completely encloses the semiconductor chip. Completelysurrounding in each case means that no opening remains. Theencapsulation can be in direct contact with the semiconductor chip orcan be spaced apart from the semiconductor chip. The encapsulation isnot restricted in terms of its geometry and can be flat or lenticular,for example. It can also have a cavity or be designed as a convex lens.The encapsulation can be, for example, a casting. For example, it canalso be a multi-stage encapsulation.

In at least one embodiment, the encapsulation comprises a polysiloxane.Polysiloxanes are in particular polyorganosiloxanes, i.e., silicones.For example, the silicone is a two-component silicone (“2K silicone”),such as thermally curable, addition-crosslinking two-component siliconesbased on dimethylsiloxane. For example, the encapsulation comprises oneor more other materials in addition to the polysiloxane. Theencapsulation can therefore comprise several materials or consist ofseveral materials. For example, the encapsulation may comprise one ormore phosphors and/or converting materials, which may be distributed inthe form of particles in the encapsulation. A converter materialconverts a primary radiation with a shorter wavelength into a secondaryradiation with a longer wavelength. For example, the converter materialmay be a material that is excited by blue light and emits yellow light.If the blue light is only partially converted into yellow light, anadditive mixture of different spectral colors can be achieved. Thisprinciple can also be used to generate white light. However, theencapsulation can also be free of phosphors and converter materials. Forexample, the encapsulation consists of the polysiloxane.

In at least one embodiment, the optoelectronic component comprises atleast one barrier layer for protection against harmful gases. Forexample, the component comprises exactly one or exactly two barrierlayers. A barrier layer is a layer which slows down or completelyprevents the permeation of harmful gases into the inside of thecomponent, in particular in the vicinity of the semiconductor chip. Forexample, a barrier layer is a layer that forms a diffusion barrier forharmful gases.

Here and in the following, harmful gases refer to gaseous substancesthat can be decomposed and deposited under the influence of radiationfrom the semiconductor chip of the optoelectronic component and/or underthe influence of heat. A deposition inside the optoelectronic component,in particular in the beam path of the component, leads to loss ofbrightness and color changes. In particular, the harmful gases areso-called VOCs, i.e., volatile organic compounds. This is a collectiveterm for organic, i.e., carbon-containing substances that evaporateeasily or are already present as a gas at low temperatures, e.g. roomtemperature. The word volatile means that the substances belonging tothe group of VOCs evaporate quickly due to their high vapor pressure orlow boiling point. For example, VOCs are organic compounds that have avapor pressure of 0.01 kilopascals or more at 293.15 Kelvin or have acorresponding volatility under the conditions of use. Because VOCscontain carbon, they can cause carbon deposition in the optical path ofthe optoelectronic component.

In at least one embodiment, the at least one barrier layer is arrangedon the encapsulation. In particular, it can be arranged directly on theencapsulation. In this case, directly arranged on the encapsulationmeans that the encapsulation and the barrier layer comprise a commoninterface.

In at least one embodiment, the at least one barrier layer ischaracterized by a lower permeability for harmful gases than thepolysiloxane contained in the encapsulation.

In at least one embodiment, the barrier layer is a plasma-polymerizedlayer, i.e., a layer deposited by means of plasma polymerization. Plasmapolymerization is a special plasma-activated variant of chemical vapordeposition (PECVD). In plasma polymerization, precursor compounds,so-called precursors, are activated in the gas phase by a plasma. Thisactivation results in the formation of ionic molecules and firstmolecular fragments in the form of clusters or chains are already formedin the gas phase. The subsequent condensation of these fragments on thecorresponding surfaces, e.g. surfaces of the encapsulation, then causespolymerization under the influence of temperature, electron and ionbombardment and thus the formation of a plasma-polymerized layer.

At least one embodiment relates to an optoelectronic componentcomprising

at least one optoelectronic semiconductor chip configured to emitradiation

an encapsulation around the semiconductor chip, wherein theencapsulation comprises a polysiloxane, and

at least one barrier layer for protection against harmful gases arrangedon the encapsulation, wherein the barrier layer is a plasm-polymerizedlayer.

This embodiment is explained in more detail below:

Polysiloxanes are characterized by a particularly good long-termstability against light and heat and are in this respect superior toother encapsulation materials such as epoxy resins. The use ofpolysiloxanes, in particular silicones, as encapsulation material thusmakes it possible to obtain optoelectronic components which have a highdegree of brightness and color stability under normal aging conditions,i.e., in the absence of harmful gases such as VOCs. In contrast,epoxides today no longer exhibit sufficient light aging stability formost applications.

While polysiloxanes hardly age at all under the influence of light andheat, they however show a comparatively high gas permeability. For thisreason, they usually do not offer sufficient protection against harmfulgases, especially VOCs. For example, most silicones have gaspermeabilities of 10 to 120 g/m²/d [g/m²/d=gram/square meter*day]. Thegas permeability of silicones based on dimethylsiloxane is also in thisrange. The gas permeability can be determined according to DIN EN ISO12572 (status: May 2017). For this purpose, the water vapor permeabilityof 1 mm thick samples is examined and the water vapor diffusion currentdensity is determined. Although the absolute gas permeability for amaterial depends on the respective gas used, differences in gaspermeability between different materials can be easily compared witheach other using the gas permeability values for water vapor, since thesame trends can be observed for VOCs and water vapor. The gaspermeability values given in the further course of the application arealso determined and given according to the measuring method mentionedhere.

Although there are also encapsulating silicones that have a slightlylower gas permeability, most of these materials show other weaknesses,such as increased light aging, which limits their use for optoelectroniccomponents such as LEDs. A reduction in gas permeability by using highlyrefractive silicones, which have a phenyl ring as a structural element,was also considered. The best materials of this type have a gaspermeability of 8 g/m²/d. However, even these materials cannot achievecomparably low gas permeabilities as epoxy resins, with about 3 g/m²/dand below.

For this reason, optoelectronic components comprising a polysiloxane asan encapsulation are more stable in the absence of harmful gases thanoptoelectronic components with other encapsulation materials. However,in the presence of certain harmful gases, such as VOCs, they rapidlylose brightness and change their color properties. Optoelectroniccomponents that have a polysiloxane as an encapsulation are thereforenot sufficiently stable against harmful gases.

The inventors have observed that optoelectronic components often comeinto contact with harmful gases and that these harmful gases lead to adeterioration of the radiation characteristics of the components.Optoelectronic components are regularly further processed after theirmanufacture. For example, they are installed in other components,machines or vehicles. Occasionally, they are also fitted with secondaryoptics. Here, the optoelectronic components can come into contact withsubstances that themselves release harmful gases, such as VOCs. Forexample, a number of adhesives, such as polyurethane-based adhesives,release VOCs. Components that are installed together with suchsubstances can absorb VOCs during operation. The VOCs permeateencapsulations containing polysiloxanes and are deposited inside theoptoelectronic component, e.g. as carbon depositions, which leads to theabove-mentioned loss of brightness and color changes.

Optoelectronic components of the embodiment described here thereforehave a barrier layer for protection against harmful gases, which isarranged on the encapsulation comprising the polysiloxane. The barrierlayer is a plasma-polymerized layer.

The properties of plasma-polymerized layers differ significantly fromthose of conventional polymer-based layers. A significant difference isthat layers obtained by plasma polymerization do not have regularrepeating units but form complex, irregular structures. Therefore, theycannot be described chemically by means of a structural formula. Thepolymer chains resulting from plasma polymerization are highly branchedand also comprise a high degree of cross-linking. This leads to aparticularly good impermeability against gases. Plasma-polymerizedlayers are therefore characterized by a particularly low gaspermeability. They form a particularly effective diffusion barrieragainst harmful gases.

Optoelectronic components of the above-mentioned embodiment are thuscharacterized by the fact that they comprise a particularly highstability against light and heat under normal conditions—i.e., in theabsence of harmful gases—and at the same time show a high stability inthe presence of harmful gases. VOCs in particular can be effectivelykept away by the plasma-polymerized layer.

Components of this type can therefore also be installed together withcomponents that release harmful gases. They can therefore also becombined with VOC-critical materials without the risk of a VOC-relateddecrease in brightness. This facilitates further processing and reducesthe risk of undesired failures of optoelectronic components. The rangeof application of the components is thus extended. In contrast,conventional components had to comply with numerous regulations duringfurther processing to avoid contact with materials that release harmfulgases. Due to the barrier layer, it is also no longer necessary todispense with polysiloxane in the encapsulation in the presence ofVOC-critical materials.

According to at least one embodiment, the optoelectronic component is alight emitting diode, or LED for short. The component is preferablydesigned to emit yellow, blue, red, orange, green or white light or UVlight.

According to at least one embodiment of the optoelectronic component, itcomprises at least one optoelectronic semiconductor chip with asemiconductor layer sequence. The semiconductor layer sequence of thesemiconductor chip is preferably based on a III-V compound semiconductormaterial. The semiconductor material is preferably a nitride compoundsemiconductor material such as AlnIn1-n-mGamN or also a phosphidecompound semiconductor material such as AlnIn1-n-mGamP, where 0≤n≤1,0≤m≤1 and n+m≤1 respectively. The semiconductor material can also beAlxGa1-xAs with 0≤x≤1. The semiconductor layer sequence can containdopants and additional components. For the sake of simplicity, however,only the essential components of the crystal lattice of thesemiconductor layer sequence, i.e., Al, As, Ga, In, N or P, are given,even if these may be partially replaced and/or supplemented by smallamounts of other substances.

The semiconductor layer sequence includes an active layer with at leastone pn junction and/or with one or more quantum well structures. Duringoperation of the semiconductor chip, electromagnetic radiation isgenerated in the active layer. One wavelength of the radiation ispreferably in the ultraviolet, IR and/or visible spectral range, inparticular at wavelengths between and including 200 nm and 700 nm,approximately between 420 nm and 680 nm, for example between andincluding 440 nm and 480 nm.

According to at least one embodiment, the optoelectronic componentcomprises a substrate, e.g. a lead frame or a ceramic substrate. Forexample, the semiconductor chip is arranged on the substrate.

According to at least one embodiment, the optoelectronic componentcomprises electrical contacts that enable a current supply to thesemiconductor chip.

According to at least one embodiment, the optoelectronic componentcomprises bonding wires.

According to at least one embodiment, the optoelectronic component is acomponent of the “flip-chip type”.

According to at least one embodiment, the optoelectronic componentcomprises at least one converter platelet.

The converter platelet contains at least one phosphor or convertermaterial that converts primary radiation of longer wavelength intosecondary radiation of shorter wavelength. For example, blue light isconverted into yellow light. For example, unconverted blue and yellowlight is superimposed, resulting in an additive mixture of differentspectral colors. For example, the component emits white light. Theconverter platelet can be arranged directly on the semiconductor chip orbe spaced apart from the semiconductor chip. It can be enclosed in theencapsulation.

According to at least one embodiment, the gas permeability of the atleast one barrier layer is 2.5 g/m²/d or less, preferably 1 g/m²/d orless, more preferably 0.1 g/m²/d or less. For example, the gaspermeability is between 0.001 g/m²/d and 2.5 g/m²/d, preferably between0.001 g/m²/d and 1 g/m²/d, more preferably between 0.001 g/m²/d and 0.1g/m²/d. The gas permeability can also be between 0.01 g/m²/d and 2.5g/m²/d, for example between 0.01 g/m²/d and 1 g/m²/d. Barrier layerswith such low gas permeabilities offer particularly good protection forthe component.

According to at least one embodiment, the at least one barrier layer ofthe optoelectronic component comprises a layer thickness of at least 10nm, preferably at least 25 nm, more preferably at least 40 nm, inparticular at least 50 nm or at least 60 nm. The thicker the barrierlayer, the more effective is the barrier effect of the layer. Layerthicknesses of less than 10 nm can result in a low protective effectagainst harmful gases. In addition, the surface to be coated maycomprise microscopic structures or roughnesses which must besufficiently overmolded. A layer thickness of at least 25 nm ispreferred, because holes (e.g. “pinholes”) in the layer can be avoidedparticularly well and a certain surface roughness of the surfaces to becoated can be compensated well. The higher the layer thickness, theeasier surface roughnesses can be compensated and closed layers can beachieved.

According to at least one embodiment, the at least one barrier layer ofthe optoelectronic component comprises a layer thickness of at most 20μm, for example at most 10 μm or at most 2 μm, preferably at most 500nm, more preferably at most 200 nm, at most 150 nm or at most 120 nm.The thinner the barrier layer, the less the barrier layer influences theradiation characteristic of the optoelectronic component. Absorption andthe consequent loss of brightness hardly occur in the aforementionedrange and decrease the more the thickness of the layer decreases.Thinner layers are also more flexible and thus adapt particularly wellto the comparatively soft and deformable polysiloxane of theencapsulation. If the polysiloxane of the encapsulation is deformed,thinner barrier layers are sufficiently flexible not to become brittledespite such deformations. The formation of cracks, which could havenegative consequences for protection against harmful gases, can thusgenerally be avoided even under mechanical stress.

According to at least one embodiment, the at least one barrier layer ofthe optoelectronic component comprises a layer thickness of 10 nm to 20μm, preferably from 25 nm to 500 nm, more preferably from 50 nm to 200,for example 60 nm to 120 nm. These can be deposited without highproduction effort, e.g. by plasma polymerization, and offer goodprotection against harmful gases. The thinner the layer, the faster thedeposition can be carried out. Thinner layer thicknesses (e.g. below 500nm) are, as already mentioned, also advantageous in order to avoid therisk of undesirable mechanical stresses in the barrier layer. At thesame time, the thinner layer thickness minimizes absorption so that thebrightness and color location of the radiation emitted by the componentis not or hardly affected. Particularly good gas impermeability combinedwith excellent optical and mechanical properties of the barrier layercan therefore be achieved, especially with layer thicknesses between 25and 500 nm, for example between 50 and 200 nm.

According to at least one embodiment, the encapsulation of theoptoelectronic component comprises at least one surface which forms anouter surface of the optoelectronic component, wherein the barrier layeris arranged directly on this surface. Preferably, the barrier layerforms the outermost layer of the optoelectronic component, i.e., a finallayer of the component to the outside.

Preferably, the at least one surface of the encapsulation comprises atleast one main beam exit surface of the optoelectronic component. A mainbeam exit surface can in particular be understood as an outer surface ofthe optoelectronic component which is located in the beam path of thesemiconductor chip and through which a larger part of the radiationemitted in total is emitted than through the other outer surfaces of theoptoelectronic component. In this case, the barrier layer is thusarranged at least on one surface of the encapsulation, which forms themain beam exit surface. For example, the main beam exit surface islocated on the outer surface of the component opposite a substrate ofthe component.

According to at least one embodiment, the encapsulation comprisesfurther surfaces forming outer surfaces of the optoelectronic component,which are side surfaces of the component and on which the barrier layeris arranged.

According to at least one embodiment, the barrier layer is arranged onlyon the surface of the encapsulation that forms the main beam exitsurface. Such optoelectronic components can be produced with aparticularly low effort.

According to at least one embodiment, the barrier layer is arranged onthe surface of the encapsulation which forms the main beam exit surfaceand additionally on the surfaces of the encapsulation which form sidesurfaces of the optoelectronic component. Preferably, the barrier layeris arranged on all surfaces of the encapsulation which form outersurfaces of the optoelectronic component. In this case a particularlyeffective protection against harmful gases is achieved.

According to at least one embodiment, the optoelectronic component has ahousing which comprises a cavity in which the at least one semiconductorchip is arranged, wherein the encapsulation comprising a polysiloxanesurrounds the semiconductor chip together with the housing. In thiscase, the plasma-polymerized layer can also be arranged on the housingin addition to the encapsulation. The housing can also be free of theplasma-polymerized layer. The materials used for housings are generallymuch more impermeable to harmful gases than polysiloxanes. It istherefore not necessary to apply a barrier layer to the housing. Apartial deposition on the housing is associated with a lower productioneffort, because in this case, covers or shading of the housing duringthe deposition of the plasma-polymerized layer can be dispensed with.

According to a preferred embodiment, at least one barrier layer of theoptoelectronic component is a plasma-polymerized siloxane layer.Preferably, the plasma-polymerized siloxane layer is arranged directlyon the encapsulation, i.e., it comprises a common interface with theencapsulation. The inventors have found that plasma-polymerized siloxanelayers are particularly suitable for protection against harmful gases.They bond particularly tightly with encapsulations comprisingpolysiloxanes. Finally, plasma-polymerized siloxane layers arecharacterized by a high degree of crosslinking and a particularly lowgas permeability. Gas permeabilities of 1 g/m²/d or less, preferably 0.1g/m²/d or less can be achieved, for example gas permeabilities of 0.001to 1 g/m²/d. Plasma-polymerized siloxane layers are furthercharacterized by a significantly higher aging stability than manyconventional plasma-polymerized layers, for example based onhydrocarbons, which predominantly comprise C—C and C—H bonds. Inaddition, plasma-polymerized siloxane layers, compared to otherplasma-polymerized layers, have a similar refractive index as typicalsilicone-based or polysiloxane-based encapsulation materials with veryhigh transparency to radiation, especially in the visible spectrum. Thetransparency of plasma-polymerized siloxane layers is usually greaterthan 90%, often greater than 92% for the visible light spectrum.Plasma-polymerized siloxanes show no or at most very little inherentcoloration. Plasma-polymerized siloxane layers can therefore be designedin such a way that they are essentially free of yellowish or evenbrownish color shades. The lower the hydrocarbon content in theplasma-polymerized siloxane layer, the lower the inherent coloration.Although plasma-polymerized siloxane layers are comparatively dense,they are still mechanically slightly flexible or ductile, so that crackformation is essentially avoided when deposited on a rather softencapsulating silicone. In contrast to, for example, purely inorganiclayers, such as pure SiO₂ layers, the coefficient of thermal expansionis also more similar to the encapsulation to be coated, so that themechanical stresses occurring during temperature jumps are also lower.The properties of plasma-polymerized siloxane layers can be furtheradjusted by precise process control. The barrier effect, the opticaltransparency, the adhesion to the encapsulation, as well as themechanical properties, e.g., the expansion coefficient and the surfaceenergy, can be further refined.

According to at least one embodiment, the barrier layer is aplasma-polymerized siloxane layer which

comprises a silicon content in the plasma-polymerized siloxane layer ofbetween 24 and 35 atomic percent,

comprises a carbon content in the plasma-polymerized siloxane layer ofbetween 5 and 50 atomic percent and

comprises an oxygen content in the plasma plasma-polymerized siloxanelayer between 23 and 63 atomic percent.

The atomic percentage values are standardized so that carbon, siliconand oxygen add up to 100 atomic percent. This means that the proportionof hydrogen in the layer is not taken into account, as the hydrogencontent of the layer cannot be reliably determined using the usualmethods. The layers naturally also contain a certain amount of hydrogen,which is present in particular in the alkyl side chains of thepolymerized siloxane. The composition can be determined by conventionalmethods, especially XPS or EDX according to the usual procedures.

The composition of the plasma-polymerized siloxane layer thus liesprecisely in a range between the compositions of pure SiO₂ and thecomposition of the precursor used (e.g., HMDSO).

A further development of the aforementioned embodiment comprises acarbon content in the plasma-polymerized siloxane layer greater or equalto 5 and less than 25 atomic percent, for example, greater or equal to 5and less than 15 atomic percent. The layer therefore is comparativelylow in carbon. In this case, the layer is comparatively hard and shows aparticularly high gas impermeability.

According to another development of the above mentioned embodiment, theplasma-polymerized siloxane layer comprises a carbon content in theplasma-polymerized layer greater or equal to 25 and less or equal to 50atomic percent. In this case, the layer is rich in carbon and thereforemore ductile. Layers of this type adapt better to the polysiloxane ofthe encapsulation.

Carbon-rich layers are relatively low in oxygen. In this case, forexample, the oxygen content of the layer can be between 23 and 40 atomicpercent. In contrast, layers low in carbon are comparatively rich inoxygen. In this case, the oxygen content of the layer can, for example,be greater than 40 atomic percent and less than or equal to 63 atomicpercent. Regardless of this, the silicon content in the layer iscomparatively constant and is always in the range between 24 and 35atomic percent in the plasma-polymerized siloxane layer, preferablybetween 28 and 34 atomic percent in the plasma-polymerized siloxanelayer.

The higher the oxygen content or the more the composition of the layerapproaches that of pure SiO₂, the harder and more gas-impermeable itbecomes. The higher the proportion of carbon (more preciselyhydrocarbon) in the plasma-polymerized siloxane layer, the less hard andbrittle the layer is.

In this case, the layer is more flexible and can therefore betterwithstand mechanical stress. If the soft polysiloxane of theencapsulation underneath the layer is deformed, the plasma-polymerizedsiloxane layer tends less to form cracks the higher the carbon contentbecomes.

According to at least one embodiment, the optoelectronic componentcomprises a plasma-polymerized siloxane layer made of a precursorselected from linear, branched or cyclic siloxanes. A precursor is astarting material, i.e., a reactant, for plasma polymerization.

According to at least one embodiment, the optoelectronic componentcomprises a plasma-polymerized siloxane layer made of a precursor of thefollowing general formula:

wherein

R¹ to R⁸ are each independently of one another selected from hydrogen,alkyl, alkenyl, and

n is selected from 0, 1, 2 and 3.

Alkyl means in particular C1-C5 alkyl, for example, methyl, ethyl andpropyl. Preferably, alkyl is methyl. Methyl groups can be easilyactivated and eliminated during plasma polymerization, which allows goodcrosslinking and rapid reaction processing.

Alkenyl means in particular C2-C5 alkenyl, for example, vinyl or allyl.Preferably, alkenyl is vinyl. Vinyl groups are functional groups whichallow an additional type of cross-linking during plasma polymerization.

n is preferably 0 or 1. Small values for n can have a positive effect onthe reaction rate, i.e., accelerate the reaction. If the values for nare too high, the precursors are also difficult to evaporate.

According to at least one embodiment, the plasma-polymerized siloxanelayer is produced from several precursors, for example, from two of theprecursors mentioned.

According to at least one embodiment, n equals 0, so that the precursorcomprises the following general formula:

wherein R¹ to R⁶ are each independently of one another selected fromhydrogen, methyl and vinyl.

Preferably, at least two of the three radicals R¹ to R³ are methyl andat least two of the three radicals R⁴ to R⁶ are methyl.

According to at least one embodiment, the precursor is selected from thegroup comprising

hexamethyldisiloxane (HMDSO),

tetramethyldisiloxane (TMDSO),

divinyltetramethyldisiloxane (DVTMDSO),

tetramethylcyclotetrasiloxane (TMCTS), and mixtures thereof.

According to at least one embodiment, the plasma-polymerized layer ischaracterized in that its deposition is carried out in a high-frequencyfield. The height of the frequency depends on the size and design of thesystem for depositing the plasma-polymerized layer and can be in thekHz, MHz or GHz range. The frequency can be between 10 kHz and 3 GHz,for example. The frequency is usually system-specific, i.e., it dependson the type of plasma deposition system (typical examples of frequenciesof different systems for plasma polymerization are 13.65 MHz, 27.125MHz, 2.45 GHz (microwave) and 10 or 40-100 kHz). Plasma-polymerizedlayers deposited in this frequency range show high degrees ofcross-linking due to the high energy input and thus low gasimpermeability.

According to at least one embodiment, the plasma-polymerized layer ischaracterized in that it is deposited with an inductively coupled plasma(ICP for short). However, other discharge types such as capacitivecoupled or microwave-induced plasmas are also conceivable.

According to at least one embodiment, the plasma-polymerized layer ischaracterized in that it is deposited at atmospheric pressure or in avacuum, for example, at a pressure of 101325 Pa, i.e., 1 atm.

According to at least one embodiment, the plasma-polymerized layer ischaracterized in that it is deposited in a vacuum, e.g., at 0.1 Pa to1000 Pa. A deposition in a vacuum enables a particularly controlled anduniform deposition. Vacuum deposition can be carried out at lowtemperatures. During such a process, the optoelectronic component isheated to a temperature of only 60 to 70° C., for example. The heatingof the component or the encapsulation on which the deposition is carriedout is due to the heat loss of the plasma. Such a process isparticularly gentle on the component and ensures a high quality of theplasma-polymerized layer.

According to at least one preferred embodiment, the plasma-polymerizedlayer is characterized in that it is deposited under atmosphericpressure, i.e., in an atmospheric plasma. Deposition in an atmosphericplasma has the advantage that it allows higher deposition rates thandeposition in a vacuum. Furthermore, deposition at atmospheric pressureallows a significantly lower amount of equipment to be used at lowercosts than deposition in a vacuum. A vacuum chamber is then notnecessary. The inventors have recognized that an excellent barriereffect of the plasma-polymerized layer can also be achieved withdeposition in an atmospheric plasma.

According to at least one embodiment, the plasma-polymerized layer ischaracterized in that it is deposited in the absence of oxygen. Forexample, the deposition can be carried out in the presence of argon. Itis also possible that the deposition is carried out only in the presenceof the precursor, without argon or any other gas being present.Deposition in the absence of oxygen results in the resultingplasma-polymerized layer comprising a lower oxygen content and a highercarbon or hydrocarbon content than when deposition is performed in thepresence of O₂. The lower the oxygen content of the atmosphere in theplasma during the deposition process, the higher the carbon orhydrocarbon content of the resulting plasma-polymerized layer and thelower the oxygen content. This is in particular applicable toplasma-polymerized siloxane layers. Plasma-polymerized siloxane layersdeposited in an atmosphere with a low oxygen content have acomparatively high proportion of alkyl side chains which are noteliminated during plasma polymerization. This leads to a good ductilityand softness of the plasma-polymerized siloxane.

According to at least one embodiment, the plasma-polymerized layer ischaracterized in that it is deposited in the presence of an oxidizinggas, in particular an oxygen-containing gas, e.g., oxygen (O₂). Thehigher the proportion of oxygen-containing gas in the atmosphere inwhich the plasma-polymerized layer is deposited, the higher the oxygencontent of the resulting layer. This is in particular applicable toplasma-polymerized siloxane layers. If the deposition of aplasma-polymerized siloxane layer is carried out at high O₂ content inthe atmosphere, only a small amount of alkyl side chains remain in theplasma polymerized layer. Consequently, the carbon and hydrogen contentof the plasma-polymerized siloxane layer is low. The elementalcomposition of the layer then approaches that of a layer of thecomposition SiO₂, although a certain proportion of carbon and hydrogencan remain in the layer in the range of a few at %. For example, theratio of precursor to oxygen at which the deposition of theplasma-polymerized layer is carried out can be between 1:1 and 1:2. Theratio refers here and in the following to the volume fluxes of theprecursor and oxygen gas flows supplied during the plasmapolymerization. The ratios can be further adjusted according to theselected system configuration. In the case of plasma-polymerizedsiloxane layers, layers with a particularly high gas impermeability canbe obtained with such high oxygen contents. These layers are similar incomposition to SiO₂, but are somewhat more ductile and less brittle thanpure SiO₂ due to a certain residual carbon and hydrogen content. Suchplasma polymerized layers are scratch-resistant and offer excellentprotection against VOCs.

According to at least one embodiment, the plasma-polymerized layer ischaracterized in that the deposition of the plasma-polymerized layer iscarried out in the presence of air. In this way, a layer with a highoxygen content can be achieved. At the same time, the deposition can becarried out with little effort and at a particularly low cost. Thismethod is also suitable for industrial scale and can be combined wellwith deposition in atmospheric plasma at atmospheric pressure.

According to at least one embodiment, the plasma-polymerized layer ischaracterized in that the ratio of precursor to oxygen during depositionof the plasma-polymerized layer is between 1:0 and 1:2, for examplebetween 1:0 and 1:1. If the ratio is between 1:0 and 1:1, the resultingplasma-polymerized layer is comparatively rich in carbon or low inoxygen and therefore comparatively soft. If the ratio is between 1:1 and1:2, the resulting plasma-polymerized layer is lower in carbon or higherin oxygen and thus harder. The flexibility or ductility of the layer cantherefore be adjusted as desired.

According to at least one embodiment, the deposition of theplasma-polymerized siloxane layer is carried out in the absence of anoxidizing gas. Then the deposition takes place e.g., in the presence ofan inert gas such as argon or alternatively only in the presence of theprecursor. In this case, a particularly high carbon content is achievedin the plasma-polymerized siloxane layer.

According to at least one embodiment, the plasma-polymerized layer ischaracterized in that during its deposition one parameter or severalparameters are varied so that the plasma-polymerized layer comprises atleast one gradient. For example, the ratio between precursor and oxygen,the pressure or the plasma power is changed. Often, however, the plasmapower is determined by the system used for plasma polymerization andremains unchanged. For the example of a plasma-polymerized siloxanelayer, a higher plasma power usually leads to a higher tendency of thealkyl side chains to be eliminated during the plasma polymerization andthe resulting layer is therefore lower in carbon or higher in oxygen. Bythe appropriate choice of parameters, for example, a gradient in theproportion of oxygen in the plasma-polymerized layer can be obtained. Asdescribed above, this is possible mainly by a suitable choice of theratio between precursor and oxygen during deposition. For example, theplasma polymerization can be started with a low O₂ content or completelywithout O₂, for example, in an atmosphere that contains only Ar besidesthe precursor. After a first part of the barrier layer with a certainthickness, e.g., 20 nm, is deposited in this way, the O₂ content can beincreased. The ratio between precursor and oxygen during deposition isthus shifted towards a higher oxygen content. This way, a gradientregarding the oxygen content in the plasma-polymerized layer is formed.In this case, the oxygen content increases from the inside to theoutside, relative to the optoelectronic component, and in the same waythe carbon and thus the hydrocarbon content decreases from the inside tothe outside. The layer is then softer on the inside than on the outside.To the outside, the barrier layer thus becomes increasingly harder andmore impermeable to gas.

According to at least one embodiment, the optoelectronic componentcomprises at least one further barrier layer, i.e., a second barrierlayer, on top of the first barrier layer. Preferably, the furtherbarrier layer is arranged directly on the first barrier layer, i.e., thetwo layers comprise a common interface. Preferably, both layers areplasma-polymerized layers, in particular plasma-polymerized siloxanelayers. For example, both layers can be deposited in the same way andthus comprise the same properties with regard to their composition andbarrier effect. Preferably, however, the two plasma-polymerized layersare deposited by varying at least one parameter during plasmapolymerization. More preferably, both barrier layers areplasma-polymerized siloxane layers, wherein the second layer isdeposited in the presence of a higher proportion of O₂ than the firstlayer. In this way, a first barrier layer is first obtained on theencapsulation comprising a polysiloxane, which still has a higher carboncontent. The first layer already comprises good barrier properties. Thesecond plasma-polymerized siloxane layer, which is deposited in thepresence of a higher O₂ content than the first layer, is finallycharacterized by a higher oxygen content in the layer and is harder,more scratch-resistant and particularly impermeable to gas. The firstbarrier layer is then softer. As described above, the plasma-polymerizedlayer is then better adapted to the underlying polysiloxane of theencapsulation. If the usually much softer polysiloxane of theencapsulation is deformed, the plasma-polymerized siloxane layerpositioned above it is then flexible enough not to break despitedeformation within certain tolerance ranges and thus not to form cracks.The second barrier layer is particularly impermeable to gas. Thecombination of these layers achieves a particularly good overallprotective effect against VOCs.

Furthermore, the surface energy or the surface properties of the layercan be adjusted by a gradient or a thin final layer (with a thickness ofsome tenths of a nm to some nm).

For example, the layer can be made hydrophilic or hydrophobic, dependingon whether the ratio of precursor to oxygen is chosen large or small. Ifthe proportion of oxygen is high (e.g., ratio of 1:1 to 1:2) the surfaceof the layer becomes hydrophilic. If, on the other hand, the oxygencontent is low or no oxygen is present during deposition, the layerbecomes hydrophobic. In this way, the properties of the layer can bedesigned as desired.

According to at least one embodiment, the plasma-polymerized layer ischaracterized in that it is deposited by means of a nozzle. This methodis suitable if the deposition is carried out using atmospheric plasma.For example, the nozzle is scanned over the optoelectronic component orover a number of optoelectronic components of the same type. This allowsa simple production with uniform deposition of the plasma-polymerizedlayer.

Embodiments further relate to a method for producing an optoelectroniccomponent. Preferably, the method described here is used to produce theoptoelectronic component described here. In particular, all explanationsmade for the optoelectronic component apply to both the method and thecomponent.

According to at least one embodiment, the method for producing anoptoelectronic component comprises the following steps:

A) providing at least one optoelectronic semiconductor chip (1)configured to emit radiation and at least one encapsulation (2) aroundthe semiconductor chip (1), wherein the encapsulation (2) comprises apolysiloxane,

B) depositing at least one barrier layer (3) for protection againstharmful gases, on the encapsulation (2) by means of plasmapolymerization.

It should be noted that all embodiments and specifications for theoptoelectronic component which relate to the deposition of the barrierlayer, in particular the plasma-polymerized layer, are valid for themethod and in particular with regard to process step B).

The method enables the production of components that are not onlyparticularly stable against light aging and heat in the absence ofharmful gases, but are also unaffected by harmful gases. The method isalso suitable for industrial scale.

According to at least one embodiment of the method, a surface of theencapsulation is pretreated or cleaned prior to step B). In this way,the layer adhesion of the plasma-polymerized layer can be improved.

According to at least one embodiment of the method, a surface of theencapsulation is pretreated with plasma prior to step B). A pretreatmentor cleaning by plasma, e.g., by means of Ar-, O₂-, N₂-, NH₃-plasma ormixtures thereof, leads to particularly good adhesion of theplasma-polymerized layer on the encapsulation. Air plasma is inparticular suitable for plasma polymerization with atmospheric plasma.Ar-Plasma is in particular suitable if the plasma polymerization iscarried out in vacuum.

According to at least one embodiment of the method, plasma pretreatmenttakes place immediately before coating. The pretreatment can, forexample, be carried out in the same system for plasma deposition as theplasma polymerization.

At least one embodiment of the method comprises the further method stepsA0) and C), wherein in step A0), which precedes step A), a plurality ofsemiconductor chips (2) are applied and attached to a substrate (7) andare provided with an encapsulation (3), and wherein in step C) thesemiconductor chips with encapsulation are separated, wherein step C) iscarried out prior to or after step B).

Separation is understood to be a segregation. Thus, the semiconductorchips with encapsulation, which each result in an optoelectroniccomponent, are separated from one another. Separation can be carried outby sawing, cutoff grinding, cutting or etching, for example. Thesubstrate, for example, can also be cut through. Alternatively, theencapsulation is cut through, but not the substrate. This creates gapsbetween the individual units, each comprising a semiconductor chip andan encapsulation. Since the substrate can be a stretchable foil, e.g., asaw foil, the distances can be increased by stretching the foil (if thesubstrate is a stretchable foil, it is also called a temporarysubstrate). The distances between the components can therefore beadjusted to achieve a coating not only on the surface of the components,but also on the side surfaces.

If the separation is carried out prior to step B), i.e., before theapplication of the plasma-polymerized layer, this leads not only tocomponents preferably being coated on the main beam exit surface of thecomponent, i.e., the surface of the encapsulation through which themajority of the radiation leaves the component, but also to the sidesurfaces of the encapsulation being coated uniformly. In this way, allsurfaces of the encapsulation, which form the outer surfaces of theoptoelectronic component, are coated with the plasma-polymerized layer.This provides effective protection against harmful gases on all sides.

If, on the other hand, separation takes place after step B), only thesurface of the encapsulation is coated, which forms the main beam exitsurface of the component. This is particularly easy to implement interms of process engineering and is less expensive. In this case, theside surfaces are not coated with the barrier layer. Because, dependingon the geometry of the component, the diffusion paths are longer whenharmful gases penetrate from the side surfaces than when they penetratefrom the main beam exit surface, with a suitable geometry of thecomponent, a coating of the main beam exit surface is often sufficientto achieve effective protection against harmful gases. In somecomponents, the semiconductor chip is also arranged in a cavity of ahousing so that the semiconductor chip is laterally already sufficientlyprotected by the housing.

According to one embodiment, the separation is carried out by punching.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages, advantageous embodiments and further developmentsresult from the exemplary embodiments described below in conjunctionwith the figures.

In the figures:

FIGS. 1A and 1B show schematic illustrations of conventionaloptoelectronic components in the presence of harmful gases.

FIG. 2 shows a schematic illustration of the drop in luminous flux of aconventional optoelectronic component with increasing operating time inthe presence of harmful gases.

FIGS. 3A to 3F show a schematic illustration of the processes inside aconventional optoelectronic component that lead to a loss of brightnessand changes in color.

FIG. 4 shows a schematic illustration of an embodiment of anoptoelectronic component.

FIGS. 5A and 5B show a schematic illustration of a conventionaloptoelectronic component and an optoelectronic component according toembodiments in the presence of harmful gases.

FIG. 6 shows a schematic illustration of an embodiment of anoptoelectronic component with two barrier layers.

FIGS. 7A and 7B show schematic illustrations of embodiments of anoptoelectronic component with one barrier layer on the main beam exitsurface and optionally additionally on the side surfaces of theencapsulation.

FIG. 8 shows an embodiment of a method for producing optoelectroniccomponents, with the plasma-polymerized layer being applied prior toseparation of the components.

FIG. 9 shows an embodiment of a method for producing optoelectroniccomponents with a deposition of the plasma-polymerized layer afterseparation of the components.

FIG. 10 shows an embodiment of a method for producing optoelectroniccomponents with a deposition of the plasma-polymerized layer prior toseparation of the components, wherein the components comprise anencapsulation in lens form.

FIG. 11 shows an experimental setup for determining the stability ofoptoelectronic components in the presence of harmful gases.

FIGS. 12A and 12B show schematic illustrations of optoelectroniccomponents after a stability test with and without depositions ofdecomposition products of harmful gases.

FIGS. 12C and 12D show photographs of optoelectronic components after astability test with and without depositions of decomposition products ofharmful gases.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

In the exemplary embodiments and figures, identical, similar orsimilarly acting elements can each be provided with the same referencesigns. The depicted elements and their proportions among each other arenot to be regarded as true to scale. Rather, individual elements such aslayers, components, devices and areas can be shown exaggeratedly largefor better representation and/or better understanding.

FIGS. 1A and 1B show schematic illustrations of conventionaloptoelectronic components (1) in the presence of harmful gases (V). Thecomponents can comprise a semiconductor chip (2) and an encapsulation(3). The components can also comprise a substrate (7), electricalcontacts (5), bonding wires (6) and converter platelets (8). After theirproduction, optoelectronic components are often processed together withmaterials that themselves release harmful gases (V) such as VOCs. Theindividual molecules of these harmful gases (V) can diffuse through theencapsulation (3) of conventional components. The inventors haverecognized that in particular silicones as encapsulation materials areparticularly permeable to many different gases. In this way, the harmfulgases can get in the vicinity of the semiconductor chip (2) anddecompose there under the influence of heat and light, especially of UVradiation or blue light. The formation of colored decomposition productsaccelerates further degradation and leads to locally increasedtemperatures as well as the absorption of blue light. The luminous fluxdecreases and a CxCy shift towards yellow can be observed. Inparticular, these processes take place when the optoelectronic componentis located in an environment that is closed to the outside, i.e., whenthere is insufficient gas exchange.

FIG. 2 shows how the luminous flux, given in flux, of conventionaloptoelectronic components changes over time in the presence of VOCs. Theoriginal luminous flux decreases with increasing operating time. This isdue to the fact that a conventional polysiloxane-based encapsulation isnot capable of permanently blocking the harmful gases. After the harmfulgases have penetrated into the vicinity of the semiconductor chip, theabove-mentioned decomposition and deposition inside the componentoccurs, resulting in the depicted decrease in luminous flux.

FIGS. 3A to 3F schematically illustrate the processes that take placeinside a conventional optoelectronic component in the presence ofharmful gases (V). FIG. 3A schematically shows the structure of asilicone, with polymer chains (P) and their cross-linking at nodes (K),as used in encapsulations. Silicones are characterized by loosely linkedpolymer chains, which have a Si—O backbone. Because of the large freevolume in the silicone network, volatile organic compounds in particularcan easily penetrate the silicone and diffuse through the silicone. Inthis way, VOCs can also reach the vicinity of the semiconductor chip,e.g., a semiconductor chip (2) that emits blue light (2) (FIGS. 3C and3D). Under the influence of such high-energy electromagnetic radiation(h·v) as well as under the influence of locally elevated temperatures(T), organic compounds begin to decompose and change color in thevicinity of the semiconductor chip (2), so that a yellowish color can beobserved at first, then a brownish color and finally blackening. Theyellowish, brownish decomposition products (Z1) absorb theelectromagnetic radiation, such as blue photons, particularly stronglyand thus accelerate local heating and thus further decomposition anddegradation. The organic compounds decompose further and finally formsolid depositions (Z2) on the surface of the semiconductor chip (FIG.3E). Finally, the entire surface of the semiconductor chip is coveredwith a brownish, black layer (Z3) of decomposition products ordepositions containing predominantly carbon (FIG. 3F). At this stage,the luminous flux drops to zero, as no more photons can penetratethrough the layer of depositions (Z3). Due to the high temperatures ofthis layer (partly T>200° C.), silicones in the vicinity of the layer(Z3) can also decompose.

FIG. 4 shows a schematic illustration of a cross-sectional view of anembodiment of an optoelectronic component (1), with semiconductor chip(2) and encapsulation (3) around the semiconductor chip (2). Theencapsulation comprises a polysiloxane. The optoelectronic component canfurther comprise bonding wires (6) which can connect the semiconductorchip (2) to electrical contacts (5). The semiconductor chip (2) can beapplied to a substrate or carrier (7) so that the encapsulation (3)together with the substrate (7) surrounds the semiconductor chip (2).The embodiment shown comprises a barrier layer (4) for protectionagainst harmful gases (V), in particular a plasma-polymerized layer (4),which is arranged on the encapsulation (3), preferably arranged on atleast one surface of the encapsulation which forms an outer surface ofthe component. For example, the outer surface may be the main beam exitsurface (3 a) of the device. The barrier layer (4) serves as a barrierto harmful gases (V) and thus slows down or prevents the degradationprocesses described above.

FIGS. 5A and 5B show a schematic illustration of cross-sectional viewsof a conventional component (FIG. 5A) without a barrier layer and anoptoelectronic component (FIG. 5B) with a barrier layer (4), both in thepresence of harmful gases (V). The barrier layer is a plasma-polymerizedlayer, in particular a plasma-polymerized siloxane layer, which can bemade of precursors such as HMDSO, TMDSO or DVTMDSO. The deposition iscarried out in a plasma or PECVD process, preferably as a low-pressureprocess. Whereas in the conventional component (1), harmful gases (V)permeate the encapsulation comprising polysiloxane (3), the barrierlayer (4) of the embodiment shown in FIG. 5B slows down or preventsharmful gases (V) from permeating into the interior of the component(1). The component may have a housing (9). Most common housing materialsare less gas permeable than encapsulations comprising silicones.Therefore, the housing does not need to be coated with the barrierlayer. The outer surface of the housing can therefore be at leastpartially free of the barrier layer. However, parts of the housing (9 a)can also be covered with the barrier layer (4). In particular, the outersurface of the component (9 a), which is a surface of the housing (9)and is adjacent to the main beam exit surface (3 a) of the component (3a), can be completely or partially coated with the barrier layer (4). Itis therefore not necessary to shade or cover the housing during thedeposition process of the barrier layer.

FIG. 6 shows a schematic illustration of a cross-sectional view of anembodiment of an optoelectronic component (1) with two barrier layers(4), (40). Two or even more barrier layers improve the protective effectagainst VOCs. The layers can be the same or different. Preferably, thetwo barrier layers differ in their composition. Further preferably, thefirst barrier layer (4) has a higher carbon content than the secondbarrier layer (40). Preferably, the second barrier layer (40) has acomposition with a higher oxygen content than the first barrier layer(4). Thus, the first barrier layer (4) is softer and more ductile andbonds particularly well with the polysiloxane of the encapsulation (3)and the second barrier layer (40) is particularly hard and impermeableto gas. This applies in each case not only to optoelectronic componentswith a housing (9) as shown in FIG. 6, but also to all otherembodiments.

FIGS. 7A and 7B show schematic illustrations of embodiments of anoptoelectronic component (1). In FIG. 7A, the barrier layer (4 a) isarranged on a surface of the encapsulation (3), which at the same timeforms an outer surface of the component (1) and represents a main beamexit surface (3 a) of the component (1). The side surfaces (3 b), on theother hand, are free of the barrier layer (4). FIG. 7B shows anembodiment in which the barrier layer (4 a, 4 b) is also arranged on theside surfaces (3 b) of the encapsulation (3). The component also has asemiconductor chip (2). The component shown in FIGS. 7A and 7B alsocomprises bonding wires (6) and electrical contacts (5). In FIGS. 7A and7B, the layer beneath the contact (5) is a temporary substrate. Thisoriginates from the production process (see temporary substrate (7) inFIGS. 8 and 9). The finished component (1) no longer contains thetemporary substrate, so that the electrical contacts (5), which are, forexample, metal contacts, form the underside of the component.

FIG. 8 shows an embodiment of a method for producing optoelectroniccomponents (1), with an application of the plasma-polymerized layer (4)before separation of the components (1). First of all, semiconductorchips (2) and an encapsulation (3) are provided. For this purpose, thesemiconductor chips (2) are preferably arranged on a temporary substrate(7) and attached to it. The encapsulation (3) can, for example, be flatencapsulated or flat molded silicone. In the embodiment of the methodshown in FIG. 8, at least one barrier layer (4) is deposited in thesubstrate composite. This means that the deposition of the barrier layer(4) is carried out before the separation of the components (1). Duringsuch a method, components (1) are obtained which are coated only ontheir upper surface, i.e., on the outer surface of the encapsulationwhich forms a main beam exit surface (3 a) of the component. Incontrast, the side surfaces (3 b) are free of the barrier layer (4). Inthis way, a component (1) is obtained as shown in FIG. 7A. Suchcomponents can be produced with less effort in terms of processtechnology. The temporary substrate (7) can be removed at the end.

FIG. 9 shows a different embodiment of a method for producingoptoelectronic components (1), with the application of theplasma-polymerized layer (4) after the separation of the components. Themethod differs from the process shown in FIG. 8 thus only in that thecomponents (1) are first separated and that only after that the barrierlayer (4) is deposited. In this way, both the main beam exit surface (3a) and the side surfaces (3 b) are coated. An optoelectronic componentas shown in FIG. 7B is obtained. Such components offer protection fromharmful gases on all sides and are therefore particularly stable. Heretoo, the temporary substrate can be removed at the end of the productionprocess.

FIG. 10 shows an embodiment of a method for producing optoelectroniccomponents, with an application of the plasma-polymerized layer (4)prior to separation of the components (1), wherein the componentscomprise an encapsulation in lens form (3). This can, for example, be aninjection-molded silicone lens. These components have side surfaces (3b) which, compared with the main beam exit surface (3 a), make up only asmall proportion of the total surface area of the encapsulation (3).Especially for components with an encapsulation in lens form (3), acoating of the side surfaces (3 b) is usually not necessary to achieve asufficient protective effect against harmful gases due to the longdiffusion paths from the side of the component to the semiconductor chip(2) and the comparatively small uncoated or unprotected encapsulationsurface. However, separation prior to coating is also possible.

FIG. 11 shows an experimental setup for determining the stability ofoptoelectronic components in the presence of harmful gases. A series ofexperiments were carried out in which conventional components weretested first. For this purpose, the component to be tested wassurrounded with a defined amount of polyurethane adhesive (12).Polyurethane adhesives release considerable amounts of VOCs. Severalexperiments were carried out with different amounts of adhesive, namelywith 3 g to 6 g. The component was finally electrically contacted andthen covered with a glass (10) so that the component could be operatedin a closed system that did not allow gas exchange with the environment.The glass thus contained VOCs that are released by the polyurethaneadhesive. Tests were carried out with beakers of different volumes(beakers with diameter×height=1.5 cm×1.35 cm; 1.0 cm×2.55 cm; 2.2 cm×4.5cm). The optoelectronic components were operated with currents of 0.1 A,1 A and 1.2 A. Each test lasted 500 h, but effects can be observed afteronly a few hours (usually significantly less than 24 h).

FIG. 12A shows the schematic illustration and FIG. 12C the associatedphotograph of a conventional optoelectronic component (1) after one ofthe tests just described. In this case, LEDs were tested. The photographstill shows the adhesive (12) that was applied around the component (1)for the test. After the test, the component was separated and thusdestroyed in order to make the depositions inside the component visible.The photograph shows the lower part of the destroyed component (1) withthe semiconductor chip (2). Further, the photograph shows the upper partwith lens and converter platelet (8). The upper part was turned upsidedown after separation so that the underside of the converter platelet (8a) is visible. As can be seen in FIG. 12A and the photograph of FIG.12C, a conventional component shows a very high level of depositions onthe underside of the converter platelet (8 a) after the test. Thedepositions have therefore been deposited near the semiconductor chip,namely at the interface between the semiconductor chip and the converterplatelet. During operation of the component tested, a sharp drop inluminous flux was also observed.

In contrast, FIG. 12B and photograph 12D show a conventionaloptoelectronic component, in which the same test was first performedusing the same conditions as in the example just mentioned (i.e.,exposure to VOCs from a polyurethane adhesive in a beaker, i.e., in aclosed system). Afterwards the beaker was removed and the component wasoperated further. In this case, it can be observed that in open systems,with sufficient ventilation, the carbon depositions are slowly removedagain. With sufficiently long operation in an open system, thebrightness can be largely restored. In the present case, the test wascontinued for several hundred hours, so that a brightness of 95% of theoriginal value could be restored. However, since many optoelectroniccomponents are permanently installed in closed systems together with,for example, polyurethane adhesives or other VOC-emitting components,there is no recovery of brightness in such cases. The inventors haverecognized this problem and solved it by the disclosed embodiments ofthe component. Experiments on components with a barrier layer, inparticular a plasma-polymerized siloxane layer, do not lead to asignificant deposition of carbons from the beginning after performingthe aforementioned test, an exposure to VOCs in a closed system (withoutsubsequent operation in an open system), and there is hardly any loss ofbrightness. Consequently, when a component is separated, the samepicture as shown in FIGS. 12B and 12D appears, namely no significantcarbon depositions and hardly any loss of luminous flux. The barrierlayer thus offers effective protection against harmful gases, so thatluminous flux, brightness and color of the component remain largelyunchanged even when operated in the presence of harmful gases. Thebarrier layer thus enables components that are particularly stable evenin the presence of harmful gases.

The exemplary embodiments and their features described in conjunctionwith the figures can also be combined with each other according tofurther exemplary embodiments, even if such combinations are notexplicitly described or shown in the figures. Furthermore, the exemplaryembodiments described in conjunction with the figures may haveadditional or alternative features according to the description in thegeneral part.

The invention is not limited to the exemplary embodiments by thedescription based on the exemplary embodiments. Rather, the inventioncomprises any new feature as well as any combination of features, whichin particular includes any combination of features in the claims, evenif this feature or combination itself is not explicitly stated in theclaims or exemplary embodiments.

The invention claimed is:
 1. An optoelectronic component comprising: anoptoelectronic semiconductor chip configured to emit radiation; anencapsulation around the semiconductor chip, wherein the encapsulationcomprises a polysiloxane; and a barrier layer for protection againstharmful gases, the barrier layer being arranged on the encapsulation,wherein the barrier layer is a plasma-polymerized siloxane layer whichis made of at least one precursor of the general formulae:

wherein R¹ to R⁸ are each, independently of one another, selected fromhydrogen, alkyl and alkenyl, and wherein n is selected from 0, 1, 2 and3.
 2. The optoelectronic component according to claim 1, wherein thebarrier layer comprises a layer thickness of 10 nm to 20 μm.
 3. Theoptoelectronic component according to claim 1, wherein the encapsulationcomprises a surface forming an outer surface of the optoelectroniccomponent, and wherein the barrier layer is arranged directly on thesurface.
 4. The optoelectronic component according to claim 3, whereinthe surface comprises a main beam exit surface of the optoelectroniccomponent.
 5. The optoelectronic component according to claim 1, whereinthe barrier layer is made of the precursor of the general formula:

wherein n equals 0 so that the precursor has the following formula:

and wherein R¹ to R⁶ are each, independently of one another, selectedfrom hydrogen, methyl and vinyl.
 6. The optoelectronic componentaccording to claim 1, wherein the precursor is selected from the groupconsisting of

and mixtures thereof.
 7. The optoelectronic component according to claim1, wherein the barrier layer is deposited at atmospheric pressure or ina vacuum.
 8. The optoelectronic component according to claim 1, whereina deposition of the barrier layer is carried out in presence of anoxidizing gas and/or in presence of an inert gas.
 9. The optoelectroniccomponent according to claim 1, wherein a deposition of the barrierlayer is carried out in presence of air.
 10. The optoelectroniccomponent according to claim 1, wherein the barrier layer is depositedin a manner in which one or more deposition parameters are varied sothat the barrier layer comprises a gradient.
 11. The optoelectroniccomponent according to claim 1, further comprising a further barrierlayer on the barrier layer, wherein the further barrier layer is also aplasma-polymerized layer.
 12. A method for producing an optoelectroniccomponent, the method comprising: providing an optoelectronicsemiconductor chip configured to emit radiation and an encapsulationaround the semiconductor chip, wherein the encapsulation comprises apolysiloxane; and depositing a barrier layer for protection againstharmful gases on the encapsulation by plasma polymerization, wherein thebarrier layer is a plasma-polymerized siloxane layer made of a precursorof the following general formulae:

wherein R¹ to R⁸ are each, independently of one another, selected fromhydrogen, alkyl and alkenyl, and wherein n is selected from 0, 1, 2 and3.
 13. The method according to claim 12, further comprising performing apretreatment or cleaning of a surface of the encapsulation prior todepositing the barrier layer.
 14. The method according to claim 13,wherein performing the pretreatment or cleaning comprises a plasmapretreatment or cleaning.
 15. The method according to claim 12, wherein,prior to providing the optoelectronic semiconductor chip and theencapsulation around the semiconductor chip, a plurality ofsemiconductor chips is applied and attached to a substrate and providedwith the encapsulation.
 16. The method according to claim 15, furthercomprising separating the semiconductor chips with the encapsulationprior to or after depositing the barrier layer.
 17. The method accordingto claim 12, wherein depositing the barrier layer comprises depositingthe barrier layer by varying one or more deposition parameters so thatthe barrier layer comprises gradient.
 18. The method according to claim12, wherein further barrier layer is deposited on the barrier layer,wherein the further barrier layer is also a plasma-polymerized layer.